Heat and creep resisting nickel alloy castings



Patented Feb. 20, 1951 HEAT AND CREEP RESISTING NICKEL ALLOY CASTINGS Albert McCoy Talbot, Fair Haven, Everett Furman, Annadale, N.

N. J., Donald Y., and Gerald Robert Brophy and Norman Boden Pilling,

ration of Delaware N. J assignors to The International Nickel Company, Inc., New York, N.

Y., a corpo- No Drawing. Application April 25, 1950, Serial No. 158,058. In Canada 6 Claims. (Cl. 148--32.5)

The present invention relates to heat-treated,

nickel-chromium-iron alloy castings eminently suitable for use at high temperatures, and more particularly to heat-treated, heat-resisting cast articles of manufacture possessing improved high temperature properties when employed for service at elevated temperatures and possessing hightemperature properties markedly superior to conventional castings heretofore employed by the art for high-temperature purposes.

In the development of casting for use at elevated temperatures, particularly for applications such as gas turbines, jet-propulsion engines, exhaust-driven superchargers, etc., the physical properties desired are high creep and oxidation resistances, and high rupture strengths coupled with high rupture elongation at the high rupture stresses. The desirable qualities of a high-temperature alloy do not consist only of good oxidation and creep resistances at service stresses and temperatures, but must also include a combination of high rupture strength and high rupture elongation, particularly so that temporary overloads can be accommodated without causing premature failure. If a material has a good rupture strength at the higher stresses, it does not follow that it possesses good creep resistance at lower stresses which normally would be encountered in service but, since both properties are necessary, the absence of one quality immediately compromises the usefulness of an alloy.

By elongation at the rupture stress and rupture elongation is meant the degree or amount of plastic flow of the metal before failure occurs and, in the data given in this specification, is expressed in terms of per cent increase over the original gauge length of the test specimens.

Standard iron-base casting com ositions, such as those containing about 25% chromium, 12% nickel and 0.35% carbon, have been most widely used as castings in the high-temperature field. These compositions possessed creep rates at 1500 F. of the order of about 1% in 100,000 hours when stressed at about 3500 p. s. i., and a stress of about 9000 p. s. i. caused rupture in 100 hours at the same temperature with approximately rupture elongation. Furthermore, these properties, which were in excess of the properties usually obtained by the art, were obtained only when the cast alloys were made with particular care.

In addition, the practice has been to use castings in the as cast or unheat-treated condition only and, in general, to limit the sizes of the castings. Where large size castings were attempted, be-

October 7, 1946 cause of high-strength requirements, it was found that they were very sensitive to thermal shock. Due to these conditions, as mentioned above, it has been the practice of the art, where high creep resistance and high rupture properties were required, to use the much more expensively alloyed wrought materials, thereby encountering a multiplicity of fabricating operations with attendant increases in manufacturing costs.

As a result, many attempts have been made to develop an alloy which could be cast and heat treated successfully to obtain good high-temperature properties and, at the same time, be

, economical to manufacture but none, insofar as we are aware, was entirely successful when carried into practice commercially.

We have discovered that the prior art shortcomings can be avoided and that new and unexpected results can be obtained by an effective combination of a number of alloying elements present in small, economical amounts in a properly proportioned nickel-chromium-iron base composition, and that these alloys can be easily and successfully heat treated to produce a particular critical structure having high-temperature properties that arefar superior to those produced in any of the prior art castings of comparable cost.

It is an object of the invention to provide nickel-base alloy castings which can be heat treated to produce a structure having markedly improved high-temperature properties on a commercial scale.

It is another object of this invention to provide castings of critical composition which, when properly heat treated, possess a particular struc ture having excellent high-temperature oxidation resistance and markedly superior creep and rupture strength coupled with excellent rupture elongation.v T

The invention also provides as an object, cast alloy articles of: manufacture having a critical composition and'structure which exhibits an improved combination of superior creep resistance,

high rupture strength and high rupture elongation at elevated temperatures'without having to resort to mechanical working, such as rolling and/or forging, to improve the properties.

It is a further object of the invention to provide heat-resisting, heat-treatable, nickel-alloy castings which, having an unusual and economical combination of small amounts of alloying elements in a properly proportioned nickel-chromn um-iron base composition and having a particular structure obtained by proper heat treatment, possess physical properties at elevated temperatures considerably superior to those of the conventional castings of comparable cost now in gen eral use for high-temperature service.

As another ob ect, the present invention contemplates providing heat-treated alloy castings of critical composition and structure particularly suitable for use at elevated temperatures which can be produced in large sizes and complicated shapes and which-possess unusual and superior resistance to warping and cracking when subjected to thermal shock.

The invention also provides special heat-resistant, heat-treated, nickel-alloy castings for use where cast structures of a minimum weight and possessing high physical properties at ,elevated temperatures are needed. Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description.

Broadly speaking, the present invention provides heat-treated, heat-resisting, economically and easily manufactured alloy castings that have unusual creep resistance and rupture strength coupled with excellent rupture elongation, for use as cast structures possessing high physical properties at elevated temperatures, e. g, from about 1300 F. to about 1600 F. The unusual overall properties of these heat-treated castings are obtained by incorporating small but critical amounts of carbon, titanium, columbium and calcium in a properly proportioned nickelchromium-iron base composition which, when properly heat treated to produce a particular metallurgical structure, makes possible the, use of stresses about 100% in excess of those formerly applied to cast materials operating in the temperature range of about 1300 F. to about 1600 F., said heat-treated castings possessing much higher orders of rupture elongation than could formerly be expected. These heat-treated castings, in addition to possessing good oxidation resistance, also possess improved resistance to warpage and cracking resulting from thermal shock. It is possible to successfully heat treat large and complicated castings having composi-. tions within the critical composition range of the present invention to obtain properties that formerly were obtained only in comparatively small, simple, expensive, high-alloy castings or in expensively alloyed, wrought materials which required complicated and time-consuming methods of fabrication. The broad and preferred ranges of composition of the heat-treated cast product embodied in the invention are set forth in Table No. l.

The iron content usually falls within the range of about to 36% of the total composition, preferably about 24% to 31%.

- treatment widely known 4' Examples of compositions falling within the foregoing ranges are as follows:

The proper heat treatment to apply to the foregoing castings within the foregoing ranges of composition in order to obtain the articular structure contemplated by the present invention is, broadly, the usual type of age-hardening heat to the prior art and, in the case of the present alloys comprises, generically speaking, a high-temperature solution treatment of the solid casting to at least above about 2200 F., preferably between about 2200" F. and about 2400 F., followed by a rapid cooling to I at least below about 1500 F., in order to maintain appreciable amounts of the precipitable phases in solution. The castings are then aged in the temperature range of about 1300 F. to about 1600 F. A preferred age-hardening treatment is the three-step type disclosed at page 3, column 2, lines 38 to 44, of the U. S. Patent No. 2,048,165 to Pilling and Merica and comprises solution treating for about one hour at about 2300 F., and waterquenching, then aging at about 1300 F. for about 12 hours, and then aging again at about 1500 F. for about 18 hours. The castings can then be cooled at any convenient rate, such as air cooling, furnace cooling, etc. In most cases, a third-ste treatment at a higher aging temperature than the prior second-step aging erases any previous effects of an aging treatment at a lower temperature and the final result is the same as if only the higher temperature alone was used. In the case of the castings contemplated by the invention, however, it is found that the lower-tem perature aging followed by th higher-temperature aging results in a permanently improved hardness that could not be obtained by a twostep aging treatment at the higher temperature alone. This three-step heat treatment, e. g., solution treating at about 2300 F. and water quenchingthen aging at about l300 F. for about 12 hours, and finally aging at about 1500 F. for about 18 hours, is. particularly effective insofar as the present castings are concerned in diminishing the magnitude of the first stage of creep as compared to the same castings which were only given the more usual two-step heat treatment. However, it should be understood that material given the two-step heat treatment has desirable properties and is about equal in most other re spects to material given the three-step heat' 'asiaee matrix substantially devoid of ferrite, a substanperature solution treatment and re-precipitated v as fine, critically dispersed particles upon subsequent aging treatment.

The improved results contemplated by the present invention are provided by alloy castings having compositions within the'present critical composition range and having, when properly heat treated, the foregoing critical structure embodied in the present invention. In other Words, the improved results contemplated by the present invention are not provided by the foregoing structure alone or by the aforesaid composition alone but are only provided by the critical combination of structure and composition embodied in the present invention. For instance, similar structures might be obtained by heat treating castings having compositions outside the aforesaid critical composition range but the improved results, namely, unusual creep resistance together with high rupture strength and excellent rupture elongation at elevated temperature-s, would not be provided by such heat-treated castings. One of the outstanding advantages of the castings having the composition and structure contemplated by the present invention is their ability to Withstand a high-temperature solution treatment in large and complicated shapes without sustaining damage. Such high-temperature solution treatment of conventional heat-resisting castings having comparable carbon content would result in embrittlement that would render the castings unfit for use. It is possible to subject all shapes and sizes of castings, having the critical combination of alloying and base elements within the composition range embodied in the invention, to drastic high-temperature solution treatment followed by an aging treatment to provide superior creep resistance coupled with markedly improved rupture strength and rupture elongation.

The actual range of the base composition is critically important. It has been found that, for optimum oxidation resistance in the temperature range of about 1300 F. to about 1600 F., a chromium content of about 17% to about 23%, preferably about 19% to about 21%, should be maintained. Within this range of chromium, variations in the base composition are limited mainly to the nickel-iron ratio. With a nickel content of about 45% to about 55%, preferably about 48% to about 52%, the best combination of creep resistance, rupture strength and rupture elongation is obtained. The data contained in Table No. 2 illustrate the effect of various nickel to iron ratios on the rupture strength and rupture elongation, all the other elements being maintained within the scope of the invention.

All the rupture data given in Tables Nos. 2, 3 and l were obtained on specimens of castings which were, in every case, given identical heat treatments, e. g., the aforementioned preferred three-step aging heat treatment, to produce similar structures contemplated by the present invention. Casting No. 2 has a nickel to iron ratio contemplated by the invention, whereas: castings No.1 and No. 3 do not.

Table No. 2

Values for Percent Composltion Rupture in 100 Casting hrs. at 1500 F.

Elon- N 1 01' Fe Cb T1 Ca 0 Stress gafion P. s. 1'. Percent 20 Bal 22 .014 53 22, 500 1 20 BaL .55 .26 019 53 16, 800 9 20 Bal. .65 40 .018 .53 12,500 24 Increasing the nickel content above the range contemplated by the invention, in addition to reducing the rupture strength to a value lower than is desirable for high-temperature application, also lowers the creep strength. Decreasing the nickel content below the range specified, while maintaining good rupture strength, nevertheless embrittles the casting to a very marked extent as evidenced by the low rupture elongation.

Varying the carbon content within the specified range of this invention has very little efiect on the properties, provided the balance of the elements are present in the right proportions. Above the upper limit of about 0.6% carbon, the castings tend to be brittle, Whereas at the lower limit of about 0.3% carbon, the rupture strength is be- .low that desired for high temperature service. Maintaining the carbon in the range of about 0.3% to about 0.6% results in a casting with superior high-temperature properties that is less sensitive to minor digressions from the specified composition ranges.

To obtain the best rupture elongation properties in the heat-treated condition, it is essential that certain minimum amounts of titanium, columbium and calcium be present in the castings.

. The importance of having both titanium and oolumbium in critical combination with calcium in the castings is demonstrated by comparing the high rupture elongation of casting No. 2 (Table No. 2) with the low order of rupture elongation of castings free from either one or both of these elements, as shown in Table No. 3.

' Table No. 3

Values for Percent Composition Rupture in lOQ Casting his. at. 1500 F.

Qa Elon- N 1 Or Fe Ch '1! Ca I C cures gafion P. s. z'. Percent 4 50 20.6 Bal. 0 0 .042 .53 15,200 4.5 5 49. 4 19. 7 Bal 0 .25 020 54 15. 00 4. 0 6 50 20 1381.. .55I 0 .024 .53 20,000I 3.0

0.036% in castings which were all hot'malleable.

Table No. 4

Values for Percent Composition Rupture 1n 100 Casting hrs. at 1500- F. No.

Ni r Fe Ob Ti Ca 0 Stress 55g 1;. s. i. Percent 21 0 52 20,300 0. 5 21 008 53 19, 200 0. 5 27 012 53 17, 200 6. 5 23 017 52 16, 500 7. 0 01.9 53 10, 800 9. 0 026 53 17", 500 14. 5 21 026 52 17, 000 16, 5 23 036 51 15, 700 14. 0

It is apparent that the calcium should be in excess of about 0.010% in order to obtain good rupture elongation in combination with high rupture strengths which, heretofore, have not been attainable with such excellent rupture elongation. Values above about 0.04% calcium result in a noticeable reduction of rupture strength and rupture elongation.

The desired rupture properties are obtained only within the broad composition range disclosed in Table No. 1, although it is possible to obtain satisfactory creep strength alone over a somewhat wider range. However, to obtain a satisfactory creep rate, certain precautions are necessary. Omitting one or both of the elements titanium and columbium, as illustrated by the castings of Table No. 3, will reduce the stress necessary to produce a creep rate of about 1% in 100,000 hours at 1500 F., from about 8000 p. s. i. to about 6000 p. s. 1. Increasing the titanium content above the amount contemplated by the invention will also reduce the creep resistance of the castings, i. e., will also reduce the stress that will produce a creep rate of 1% in 100,000 hours at 1500 F.

The high creep strength of the heat-treated castings embodied in the present invention is obtained only when these castings are properly heat treated to produce the particular structure referred to hereinbefore. alloy castings in the unheat-treated or as cast condition will be approximately one hundred times the creep rate of the heat-treated alloy castings having the particular structure contemplated by the present invention. For instance, a stress of 8,000 p. s. i. at 1500 F. will produce about 1% creep in 100,000 hours in the properly heat-treated alloy castings embodied in the present invention, whereas the same stress at the same temperature will produce about 100% creep in 100,000 hours in the as cast or unheattreated castings.

The present invention is particularly applicable in cases where it is necessary or, desirable to employ cast articles at elevated temperatures under stress. Such cases include precision and centrifugally cast products and include applications such as gas turbines, including exhaust driven superchargers and turbo-jet engines, e. g., buckets, blades, rotor disks, vanes, manifolds, combustion chambers; parts of internal combustion engines, e. g., valves and valve parts; furnace parts, e. g., heat treating furnace conveyors, conveyor rolls, brackets and supports; etc., where superior high-temperature properties, such, as

The creep rate of the the maintenance of dimensions under high 's tresses inthe temperature range of about 1300 F. to 1600 F., are required.

The present application is a continuation-inpart of applicants" co-pending application U. S. Serial No. 715,622, filed December 12, 1946, now abandoned.

Although the present invention has been described in conjunction with certain preferred embodiments, it is to be understood that modifications and variations thereof may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications are to be considered within the purview of the application and the scope of the appended claims.

- We claim:

1. An article of manufacture subjected in use.

to stress at elevated service temperatures above about 1300 F. comprised of a heat-treated alloy casting containing about to nickel, about 17% to 23% chromium, about 0.25% to 1% columbium, about 0.05% to 0.5% titanium, about 0.02% to 0.03% calcium, about 0.3% to 06% carbon and the balance substantially iron; and having a heat-treated structure containing an austenite matrix substantially devoid of ferrite, a substantial amount of fine secondary precipitate critically dispersed throughout said matrix and some relatively large primary precipitate scattered throughout said matrix.

2 An article of manufacture subjected in use to stress at elevated service temperatures above about 1300" F. comprised of a heat-treated alloy casting containing about 48% to 52% nickel, about 19% to 21% chromium, about 0.4% to 0.8% columbium, about 0.2% to 0.3% titanium, about 0.02% to 0.03% calcium, about 0.40% to 0.55% carbon and the balance substantially iron; and having a heat-treated structure containing an austenite matrix substantially devoid of ferrite, a substantial amount of fine secondary precipitate, critically dispersed throughout said matrix and some relatively large primary precipitate scattered throughout said matrix.

3. An article of manufacture subjected in use to stress at elevated service temperatures above about 1300 F. comprised of a heat-treated alloy casting containing about 45% to 55% nickel, about 17% to 23% chromium, about 0.25% to 1% columbium, about 0.05% to 0.5% titanium, about 0.01% to 0.04% calcium, about 0.3%. to 0.6% carbon and the balance substantially iron;

' and having a heat-treated structure containing an austenite matrix substantially devoid of ferrite, a substantial amount of fine secondary precipitate critically dispersed throughout said matrix and. some relatively large primary precipitate scattered. throughout said matrix.

4. A heat-treated casting for use at elevated service temperatures above about 1300 F. comprised of an alloy casting containing about 48% to 52% nickel, about 19% to 21% chrocrnium, about 0.4% to 0.8% colurnbium, about 0.2% to 0.3% titanium, about 0.02% to 0.03% calcium, about 0.40% to 0.55% carbon, about 0.1% to about 2.0% manganese, about 0.2% to about 1.5% silicon, and the balance substantially iron; and having a heat-treated structure containing an austenite matrix substantially devoid of ferrite, a substantial amount of fine secondary precipitate critically dispersed throughout said matrix andsome relatively large primary precipitate scattered throughout said matrix.

5. A heat-treated casting for use at elevated service temperatures above about 1300 F. comprised of an alloy containing about 45% to 55% nickel, about 17% to 23 chromium, about 0.25% to 1% columbium, about 0.05% to 0.5% titanium, about 0.01% to 0.04% calcium, about 0.3% to 0.6% carbon, about 0.1% to about 2.0% manganese, about 0.2% to about 1.5% silicon and the balance substantially iron; and having a heattreated structure containing an austenite matrix substantially devoid of ferrite, a substantial amount of fine secondary precipitate critically dispersed throughout said matrix and some relatively large primary precipitate scattered throughout said matrix.

6. An article of manufacture subjected in use to stress at elevated service temperatures above about 1300 F. comprised of a heat-treated cast alloy containing about 45% to 55% nickel, about 17% to 23% chromium, about 0.25% to 1% columbium, about 0.05% to 0.5% titanium, about 0.02% to 0.03% calcium, about 0.3% to 0.6% carbon, about 0.1% to about 2.0% manganese, about 0.2% to about 1.5% silicon and the balance substantially iron; and having a heat-treated structure containing an austenite matrix substantially devoid of ferrite, a substantial amount matrix.

ALBERT MCCOY TALBOT. DONALD EVERETT FURMAN. GERALD ROBERT BROPHY. NORMAN BODEN FILLING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 15 Number a Number Name Date Lohr June 18, 1935 Lohr Nov. 5, 1935 Pilling July 21, 1936 Feussner July 21, 1936 Prosen Aug. 30, 1938 Rohn July 1, 1941 Clarke Aug. 24, 1948 Clarke Aug. 24, 1948 FOREIGN PATENTS Country Date Great Britain June 29, 1935 

1. AN ARTICLE OF MANUFACTURE SUBJECTED IN USE TO STRESS AT ELEVATED SERVICE TEMPERATURES ABOVE ABOUT 1300* F. COMPRISED OF A HEAT-TREATED ALLOY CASTING CONTAINING ABOUT 45% TO 55% NICKEL, ABOUT 17% TO 23% CHROMIUM, ABOUT 0.25% TO 1% COLUMBIUM, ABOUT 0.05% TO 0.5% TITANIUM, ABOUT 0.02% TO 0.03% CALCIUM, ABOUT 0.3% TO 0.6% CARBON AND THE BALANCE SUBSTANTIALLY IRON; AND HAVING A HEAT-TREATED STRUCTURE CONTAINING AN AUSTENITE MATRIX SUBSTANTIALLY DEVOID OF FERRITE, A SUBSTANTIAL AMOUNT OF FINE SECONDARY PRECIPITATE CRITICALLY DISPERSED THROUGHOUT SAID MATRIX AND SOME RELATIVELY LARGE PRIMARY PRECIPITATE SCATTERED THROUGHOUT SAID MATRIX. 